The present invention relates to an apparatus for eliminating the flutter of a paper web in a double fabric configuration in the dryer section of a papermaking machine. The operational speeds of papermaking machines have increased continuously over the recent years and are already approaching 1600 m/min. Thus, the flutter of a web will become a serious problem impairing the performance of a papermaking machine. The support of a web from a press section to a dryer section within a single fabric run is controllable by prior known technology but, within a double fabric run, especially in a first double fabric configuration, problems have been encountered at high running speeds.
In a double fabric run, a web is adapted to travel along a tortuous path between cylinders included in two tiers such that the web is always supported against the dryer cylinders of the same tier by means of one and the same dryer fabric. Thus, a double fabric each configuration includes two fabrics for supporting a web against the cylinders of a corresponding tier. Hence, the web will have long open draws when advancing from one tier of cylinders to the next. These open draws are susceptible to fluttering as a result of air currents produced by the moving parts of a dryer configuration. Efforts have been made to eliminate this problem by reducing the lengths of open draws with suitable arrangements of cylinders and their fabric guide rolls controlling the fabrics between the cylinders and by means of various blow boxes included in such open draws.
There is a prior known solution, wherein the fabric guide rolls controlling a dryer fabric between cylinders of one and the same tier are re-located on a tangential line between the cylinders such that the dryer fabric is able to escort a web as far as possible, that is the web shall not separate from the fabric until the point, at which the fabric winds around the periphery of a fabric guide roll. A pocket thus formed by the roll and the fabric is provided with a blow box, whose nozzles are used for creating a vacuum over a fabric section between the dryer cylinder and the fabric guide roll for retaining the web in contact with the fabric and for blowing air through the free section of a fabric located on the other side into a pocket on the other side. The apparatus includes three nozzles which, in view of producing air currents caused by a moving fabric and a roll, require a major amount of air which can amount up to 1400 m.sup.3 h/lateral meter. The large amount of air leads to complicated and expensive assemblies. The air to be blown is either compensation air or a mixture of compensation air and return air.